Yes, European missile defense system is in the United States' interests, because a strong Europe improves stability, which will in turn help the United States. For the most part, a strong defense system is not a threat to another nation, because it is a defensive system. Every nation should have the ability to defend itself, and doing so does not threaten anyone else.
Building a missile defense system in Eastern Europe to encircle Russia is not going to further America's interest, especially because it will simply escalate tensions and may one day most horrifyingly enough lead to a war. Antagonizing other nations does not serve US interest, and we have to acknowledge that this isn't the Cold War anymore.